The present invention relates generally to methods and apparatus for sulfonating an organic reactant with a gaseous sulfonating agent comprising sulfur trioxide (SO.sub.3), and more particularly to such a sulfonating method and apparatus employing a venturi.
Many of the considerations involved, generally, in sulfonating a liquid organic reactant with a gaseous sulfonating agent comprising sulfur trioxide are discussed in Brooks et al. U.S. Pat. No. 3,427,342, issued Feb. 11, 1969, entitled "Continuous Sulfonation Process," especially Cols. 6-14, and the discussion therein is incorporated herein by reference.
As used herein, the term "organic reactant" refers to those materials, conventionally in liquid form, which heretofore have been subjected to a sulfonating reaction employing sulfur trioxide. A description of such materials is contained in said Brooks et al. U.S. Pat. No. 3,427,342, at Cols. 6-7, and said description is incorporated herein by reference.
The term "gaseous sulfonating agent comprising sulfur trioxide" refers to those gaseous agents which have heretofore been used to sulfonate organic reactants with sulfur trioxide, usually a dilute mixture of sulfur trioxide in an inert gas such as air. Examples of such gaseous agents and of procedures for preparing sulfur trioxide are described in said Brooks et al. U.S. Pat. No. 3,427,342 at Col. 7, and that description is incorporated herein by reference.
As used herein, the term "sulfonating" is used sometimes in its generic sense, applying to both true sulfonating and sulfating, and sometimes in its specific sense applying only to true sulfonating. The actual meaning intended will be apparent to those skilled in the art from the context in which the term is used.
Typically, a venturi comprises a tubular member having an approach zone with side walls converging in a downstream direction toward a throat or constriction which is the narrowest point of the venturi. Downstream of the throat is a recovery zone having side walls diverging from the throat. A fluid flowing through a venturi is accelerated and undergoes a pressure drop in the approach zone. In the venturi throat, the velocity is higher and the pressure lower than upstream thereof.
In a sulfonating reaction employing a venturi, the organic reactant and the gaseous sulfonating agent are reacted while flowing through the venturi, and the sulfonating reaction generates a large amount of heat in the venturi which can burn and discolor the reaction product, usually a sulfonic acid or alcohol sulfonate. A charred or discolored reaction product is usually undesirable, especially where the reaction product is to be used in the manufacture of detergents. It is also possible that particles of liquid reaction product may adhere to the walls of the venturi which also could cause undesired charring and discoloration of the particles of reaction product.
Other considerations arising when sulfonating in a venturi include obtaining a high yield (i.e., converting the highest possible percentage of organic reactant into reaction product) and processing large volumes of material without sacrificing quality or yield.